ndg/lib/lvgl/docs/widgets/core/roller.md

Roller (lv_roller)

Overview

Roller allows you to simply select one option from a list by scrolling.

Parts and Styles

• LV_PART_MAIN The background of the roller uses all the typical background properties and text style properties. style_text_line_space adjusts the space between the options. When the Roller is scrolled and doesn't stop exactly on an option it will scroll to the nearest valid option automatically in anim_time milliseconds as specified in the style.
• LV_PART_SELECTED The selected option in the middle. Besides the typical background properties it uses the text style properties to change the appearance of the text in the selected area.

Usage

Set options

Options are passed to the Roller as a string with lv_roller_set_options(roller, options, LV_ROLLER_MODE_NORMAL/INFINITE). The options should be separated by \n. For example: "First\nSecond\nThird".

LV_ROLLER_MODE_INFINITE makes the roller circular.

You can select an option manually with lv_roller_set_selected(roller, id, LV_ANIM_ON/OFF), where id is the index of an option.

Get selected option

To get the index of the currently selected option use lv_roller_get_selected(roller).

lv_roller_get_selected_str(roller, buf, buf_size) will copy the name of the selected option to buf.

Visible rows

The number of visible rows can be adjusted with lv_roller_set_visible_row_count(roller, num).

This function calculates the height with the current style. If the font, line space, border width, etc. of the roller changes this function needs to be called again.

Events

• LV_EVENT_VALUE_CHANGED Sent when a new option is selected.

See the events of the Base object too.

Learn more about Events.

Keys

• LV_KEY_RIGHT/DOWN Select the next option
• LV_KEY_LEFT/UP Select the previous option
• LY_KEY_ENTER Apply the selected option (Send LV_EVENT_VALUE_CHANGED event)

Example

.. include:: ../../../examples/widgets/roller/index.rst

API

.. doxygenfile:: lv_roller.h
  :project: lvgl